Google Apps is used by more than 40 million people and signs up 5,000 new businesses every day according to numbers recently cited by Google Executive Chairman Eric Schmidt.

But what do all those millions of people actually use Google Apps for, and how heavily do they use it?

At Spanning we have a unique view into the data, so we decided to run some numbers and find out.

You can do a lot with Google Apps. It includes email, calendaring, web-based productivity apps for word processing, spreadsheets, and presentations. It allows you to upload and share documents of any type. And it’s either cheap or free, depending on which edition you choose.

Spanning Backup for Google Apps backs up Google Apps data for thousands of businesses and thousands more individuals, which affords us a unique perspective on how people actually use Google Apps. And when we looked into it, we were surprised at some of what we found.

Dropbox for the Enterprise?

The thing that jumped out at us first was that Google Docs is just as much a replacement for Dropbox as it is for Microsoft Office. Just over half (53.2%) of the documents stored by users in our sample were plain old files: PDF’s, songs, movies, photos, Microsoft Office files, etc. The rest (46.8%) were “native”, i.e., created by the web-based Google Apps spreadsheet, presentation and word processing apps.

Maybe this shouldn’t come as a surprise given Google’s emphasis on sharing and collaboration in addition to productivity, but when the press writes about Google Docs or when people in the industry talk about it, it’s often positioned as an alternative to Microsoft Office. The numbers tell a dramatically different story.

Google Docs is, in fact, an easy, cheap and secure way to share files—of any type—publicly or privately. And as it turns out, the “non-native” files people store most frequently are PDF’s, images, and Microsoft Office documents. People are storing business documents.

Bottom line: in addition to its web productivity apps, Google Docs is a lot like Dropbox for businesses.

Super Ultra Mega Power Users

The second pattern that emerged from the data had to do with the sheer amount of critical business data people store in Google Apps. Keep in mind that Google Apps is more than just Docs; it also includes Calendars and Contacts. When we looked at the usage patterns for those apps we again uncovered some interesting trends.

We knew that some heavy users had run into the limits of what Google allows. For instance, venture capitalist Brad Feld “bitched loudly” (his words) that he had more contacts than Google’s limit of 10,000—and Google quickly raised that limit to 25,000. (Full disclosure: Brad is a partner at Foundry Group, an investor in Spanning.) But we were surprised to learn that only 0.7% of the users in our sample have taken advantage of that new higher limit. The rest still have fewer than 10,000 contacts, and the average user has far fewer: 230.

Similarly, some power users store a tremendous amount of data in Google Calendar. One user had 528,767 events spread across hundreds of calendars (thanks to Google’s simple but powerful calendar sharing capabilities). But the average user had 533 events.

The data for documents and collections of documents tell a similar story. A handful of power users had over 25,000 documents and more than 10,000 document collections (folders). But the average user had just 43 documents and 10 collections.

Bottom line: Google Apps scales to meet the needs of normal people and ultra power users alike, all at the same low (or in some cases free) price point. However, the assumption that heavy usage is the norm has been debunked. The average user barely even scratches the surface of the storage capabilities available to them.

Google Apps is growing fast but will soon be battling credible threats from Microsoft Office 365 and Apple’s iCloud, among others. We’ll continue to study the trends in the data we see. Stay tuned for more reports from the front.